4. Mount a fresh drop of yeast on a slide and treat with a drop 

 of iodine. What is the effect on the cells? Is starch present in 

 the fluid? Is there any starch in the cells themselves? 



Make drawinys of the yeast cells slura'iin/ the effect of the 

 reagents. 



C. PHYSIOLOGY. 



In the following experiments the amount of growth which has 

 taken place may be roughly measured by the increase of the tur- 

 bidity in the liquid. It may be tested microscopically by the number 

 of buds to which the cell has given rise. 



1. Effect of food supply upon growth. Take five test tubes 

 each one-third full of the solution named: (a) distilled water; 

 (b) 10 per cent solution of sugar in water; (c) Pasteur's solution 

 without suger; (d) Pasteur's solution with sugar; (e) Mayer's 

 pepsin solution. 



Carefully label each tube and put a drop of yeast into each ; shake 

 the tubes thoroughly and tightly plug the month of each with a 

 wad of clean absorbent cotton and set them in the incubator, heated 

 to 35 degrees C, for two or three days. Examine the tubes from 

 day to day and judge, from microscopic examination and the tur- 

 bidity, in which fluid the ,yeast grows best. In which are the most 

 bubbles of gas formed ? Does the formation of gas bear any re- 

 lation to the growth ? 



2. Reproduction, (a) Budding. With the microscope examine 

 cells from each of the test tubes. In which have the cells the 

 largest number of buds ? In which the smallest ? How many buds 

 may a cell have ? Show by drawings the steps in the formation of 

 a mature bud. What is the difference between budding and fission ? 

 ( b ) Endogenous Spore Formation may sometimes be observed 

 in yeast which has been kept for sometime under unfavorable con- 

 ditions, e. g. lack of food, moisture, etc. 



3. The effect of growth of yeast upon food supply. ( a) Taste of 

 the 10 per cent sugar solution after yeast has been growing in it 

 for a day or two. Compare with a solution in which there is no 

 yeast. How do you explain the difference? (b) Examine the 

 distillate of a solution of sugar in which yeast has been growing 

 for a day or two. Notice that it has the taste and odor, and burns 

 with a pale blue flame, characteristic of alcohol, (c) Xature of the 

 gas given off. Take two test tubes, fill the first y$ full of clear 

 baryta water, fill the second about l / 2 full of yeast which is actively 

 giving off bubbles of gas. Insert a cork in this second tube and 



